Ultimately - personal preference.
Spools (PMR) are generally quieter but less efficient (air). Also generally require a bit more maintenance - but it's not that hard!
Poppets (Etek) are louder and more air efficient. Very easy to maintain - bolt can be cleaned and re-lubed in well under a minute. That said, bolt/rammer maintenance on the Etek or Bolt maintenance on the PMR are both really easy. Also, I found the LPR maintenance on the Etek/Ego's easier than on the PM/DM series.
Either way - both are good, reliable markers and should be good buys (if they've been looked after).